I was re-(re-re-re-re-)watching The Social Network a couple of days ago and one of the lines jumped out at me. Well, actually, all of the lines jumped out at me—oh, you and your snappy dialogue, Aaron Sorkin—but especially when Justin Timberlake, playing entrepreneurial roller coaster Sean Parker, explains that despite founding Napster, he was dead broke because “there’s not a lot of money in free music.”

While that was undoubtedly true in the days of Napster’s brave Lewis and Clark quest into the copyright wilderness, fending off vicious packs of feral Ulrichs, it looks like we’re edging closer to the point where the way we consume music has changed completely. In essence, iTunes isn’t much more than the online equivalent of a giant Sam Goody’s; but something like Spotify, which has finally made its debut in the United States after massive success overseas, signals many more possibilities.

The program isn’t shockingly new from things we’ve seen before—sites likes Grooveshark and Pandora gave us access to tons of songs for free, as well—but Spotify has an easy, Facebook-compatible system that encourages sharing. Structured around playlists, it allows users to build their own, pass them along to friends, and then trawl through those friends’ collections for songs they like.

In terms of content, Spotify says they have 15 million songs, but, in the words of Aaliyah, that ain’t nothing but a number. Importantly, that figure includes songs and albums that people care about right now, like the new Beyoncé and Lady Gaga. There’s also variety: Just tooling around this afternoon, I found an extensive array of artists, along a ton of different axes, from Katy Perry to Panda Bear, Ke$ha to Tchaikov$ky, Bird to Birdman. Not everything is available just yet. For example, there a big, soulful hole where Adele’s 21 should be, even if they do have her previous album.

Here are the limitations: The basic free service—which, presumably, is what most will use—is ad-supported, and you are restricted to 20 hours per month. You can pay $4.99 a month for unlimited listening without ads, or $9.99 to stream on mobile devices, but the program is still impressive even if you aren’t Rich Uncle Pennybags. Free Spotify is invite-only at this point, but since early adopters get a free six months of unlimited service, it’s hard to imagine that it won’t gain quick traction over here as it already has done in Europe, where it has racked up more than 10 million registered users.

The program also allows syncing to your iPod, iPhone, and Android, which takes a bite out of iTunes’ functionality. Like I said, it’s not mind-blowingly new, but it’s still one of the best (legal) music-consumption systems we’ve seen so far.